The Urushi Circuit - Use of a Traditional Craft Material for HCI -

Abstract We propose a novel electric circuit that uses urushi lacquer to construct devices for human-computer interaction (HCI). Urushi has many interesting features. Among them, we focus on its insulating properties and susceptibility to ultraviolet (UV) radiation. We postulated that a UV laser could be used to remove urushi locally, and that several layers could be connected via removed points. This made it possible to fabricate an urushi-based multilayered electronic circuit (an urushi circuit). In this paper, we propose a method for producing an urushi circuit, and verify the feasibility of our method. In addition, we constructed a prototype multilayered electronic circuit and touch sensor.

Author Keywords Urushi; Traditional Craft; Electronic Circuit; Touch Interface

ACM Classification Keywords H.5.2. User Interfaces: Theory and methods

Introduction This study proposes an interface made with urushi, which is used in traditional Japanese crafts. Urushi is a natural material that is obtained from the trunk of the Japanese lacquer tree (Toxicodendron vernicifluum). It has many features, such as resistance to heat, acids,

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Yuki Hashimoto University of Tsukuba 1-1-1 Tennnoudai, Tsukuba Ibaraki, 305-8573 Japan hashimoto@iit.tsukuba.ac.jp Naoya Koizumi The University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo, 113-8656 Japan koizumi@nae-lab.org Yu Myojin University of Tsukuba 1-1-1 Tennnoudai, Tsukuba Ibaraki, 305-8573 Japan myojin@vrlab.esys.tsukuba.ac.jp

Buntarou Shizuki University of Tsukuba 1-1-1 Tennnoudai, Tsukuba Ibaraki, 305-8573 Japan shizuki@cs.tsukuba.ac.jp Nobuko Hanada University of Tsukuba 1-1-1 Tennnoudai, Tsukuba Ibaraki, 305-8573 Japan hanada@kz.tsukuba.ac.jp

water, and humidity, it is an adhesive, and has also been used for insect proofing and as electric insulation (Table 1).

Waterproof Good Chemical resistant Good Electrical insulator High Corrosion resistant Good Adhesive High Hard Same hardness as iron Antimicrobial High Heat resistance 120–300°C Air conductivity Good Environmental adaptability Good Allergenic None

Table 1. Features of Urushi.

Technology developments allow urushi lacquer to be used on any type of material. Consequently, it is used for art, tableware, furniture, ships, building, and many other purposes. Our target areas are wearable computing and ubiquitous computing. Some wearable-computing research is studying health management to improve the quality of life (QOL) [1]. Because such wearable computing systems make use of skin contact to monitor human health [2], some of these interfaces are used in delicate areas, such as the teeth and mouth [3-6]. Therefore, the material used for these interfaces must be safe for humans. Here, we propose a new electronic device that combines urushi and electronic circuits. The Japanese lacquer urushi has many excellent properties, as summarized above. It is an electrical insulator, has antibacterial properties, and is

non-allergenic after it has dried. Furthermore, urushi can be applied to almost any material, such as plastic, glass, metal, or paper, making it suitable for wearable computing devices.

Here, we propose a method of fabricating an urushi circuit and report the results of an experiment conducted to verify the feasibility of our method with a prototype urushi circuit. We also consider the future of urushi circuits.

Method Urushi resin is composed mainly of urushiol, which is an oily organic material found in plants in Asia. It can be dissolved by ultraviolet (UV) light, as urushiol contains two double bonds that react on exposure to UV light in an oxidation reaction. This reaction changes the color, gloss, and electrical resistance of urushi. Based on this phenomenon, we propose the fabrication of a multilayered urushi circuit by removing urushi locally.

Our method is as follows (Figure 1).

1. Lacquer urushi on a base material

2. Print a circuit pattern using an electric conductor

3. Lacquer urushi on the electric conductor

4. Make through holes by dissolving the urushi using a UV laser

5. Print a circuit pattern using an electric conductor and connect it to the lower layer

6. Attach electronic parts to the circuit pattern

7. Cover the electronic parts with urushi as needed

Figure 1. Fabrication of an urushi circuit.

The main advantages of this method are that it is a contactless process and involves high working accuracy. A machining method using a drill or knife would damage the entire urushi surface by causing cracks or bending. In comparison, a UV laser dissolves only the irradiated area, without contact and we can control the power, diameter, and direction of the laser precisely [7]. Consequently, we believe that our method has the potential to fabricate very accurate urushi circuits approximately the same as those of current laser-processing machines.

Verifying Our Method To verify our fabrication method, we irradiated urushi on a copper board using a UV laser (405 nm, 200 mW, ray diameter =1, 2, and 3 mm). The distance between the UV laser and urushi was 5 mm (Figure 2). The urushi was about 10 μm thick. We checked the continuity of the irradiated area every 1 minute of irradiation. If urushi is dissolved completely, the irradiated area will short-circuit.

Figure 2. Diagram of the experiment.

The experiment showed that the UV laser could dissolve the urushi quickly (Table 2, Figure 3). The dissolving time was inversely proportional to the diameter of the ray. It was possible to control the dissolution rate by changing the power of the ray.

Irradiation time with the UV laser [min] 1 2 3 4 5 6

Diameter irradiated [mm]

1 X X X O O O 2 X X O O O O 3 O O O O O O

X: insulation; O: conduction

Table 2. The time taken for conduction.

Figure 3. Area irradiated by the UV laser.

Prototyping Two-Layer Circuit We developed a prototype to verify the possibility of fabricating a multilayer circuit using urushi. The

prototype circuit consisted of two layers of urushi. The bottom layer was used to coat a copper plate, which was connected to the ground (GND). We removed part of the urushi with a UV laser to connect the GND to the upper layer, and painted silver (Ag) ink on the bottom layer. The top layer included some electronic parts and Ag ink. We also removed the urushi in several areas using the UV laser to connect them to the GND. The circuit was used to control the brightness of two light-emitting diodes (LEDs) via variable resistance (Figure 4). We confirmed that this circuit worked as expected (Figure 5).

Touch Interface Based on the above result, we designed a touch interface with an urushi circuit. Urushi has a comfortable moist feeling. Therefore, a touch interface made with an urushi circuit should enhance the touch interaction.

We propose two types of touch sensor (Figure 6). One we call “Makie”, in which a conductor pattern is printed on the urushi. This conductor is not only an image but also a capacitive sensor. The other, we call “Cover”. In this type, the circuit pattern is covered with urushi. We can enjoy the texture and glossiness of the urushi because the circuit pattern is hidden. Furthermore, we can choose the degree of transparency and color of the urushi and decorate the surface with several types of urushi.

First, we attempted to develop the two types of touch sensor (Figure 7). The base material used was an acrylic plate. After lacquering, we printed Ag ink on the urushi using silk-screening.

Figure 4. Circuit diagram.

Figure 5. A two-layer urushi circuit.

To verify the utility of the urushi-based touch sensor, we connected sensors to a touch-detecting circuit built on a bread board (Figure 8). This circuit checked the change in the capacitance of the sensor. When touched, the capacitance changed significantly. The circuit detected this change and turned on three LEDs. The detecting test confirmed that both touch sensors could detect the touch of a finger (Figure 9).

Next, we combined the two-layer urushi circuits and urushi-based touch sensor via a detecting circuit (Figure 10). In this system, we replaced the three LEDs on the bread board with a two-layer urushi circuit. Then, two LEDs on the urushi circuit would light on touching the urushi-based touch sensor. We confirmed that this system worked. Consequently, we achieved input and output with an urushi circuit.

Figure 6. The proposed touch sensors.

Figure 7. The prototype touch sensors.

Figure 8. The proposed touch interface.

Figure 9. Detecting touch using the proposed touch sensor.

Figure 10. Combination system.

Future Impact Urushi not only has decorative beauty but it also has many useful features, is resistant to the environment, and is harmless to humans when dry. We Japanese have used it for thousands of years. Using these features, we anticipate devising urushi circuits for different applications from conventional circuits. Some possible applications are listed below.

Current uses of urushi with new functions

Urushi lacquer is already used to coat many goods in regular use, and furniture. It would be possible to add a new function to a lacquered item by adding a circuit without changing its appearance and the cost should be low.

Attractive circuits

Urushi surfaces are very beautiful and the material adds artistic value to the object that it covers. In addition, metal patterns can be placed on an urushi surface using the chinkin and makie methods. The chinkin method involves engraving grooves in the lacquer and filling them with gold leaf or powdered gold. The makie method sprinkles gold or silver powder on a picture drawn with lacquer. In addition, circuit patterns themselves are works of art [8, 9]. By combining our technique and gold decoration, we believe that new interactive art can be developed, like the urushi musical interface [10]. The urushi and gold are used to achieve both aesthetic beauty and functionality. The black lacquered surface of the instrument is decorated with gold inlay using the chinkin technique. The gold inlay is a conductive surface, and touching it turns the instrument on. In the future, makie will serve as an actual electronic circuit and enhance the value of electronic devices so that such devices will be loved.

Safe electronic equipment to the touch

Hardened urushi is antibacterial and does not cause allergic reactions. Therefore, it can be used to build toys for children, tableware, and furniture. We hope that people will love urushi products and develop a new urushi culture in the future.

Personal fabrication with urushi

In the next 10 years, we would like to spread the use of urushi for fabrication. The time of “do it yourself” (DIY) and personal fabrication is coming. Three-dimensional (3D) printers and laser cutters are contributing to

realizing a new DIY life style. These systems will help us to produce versatile new implementations for researchers, engineers, and hobbyists. Some cafes in Tokyo have installed laser cutters and 3D printers. This shows that DIY is now fashionable entertainment. We hope to increase the usable materials for personal fabrication to boost this movement. Liquid urushi can cause rashes in some people, although new types of urushi seldom cause a rash. Neither of the authors has ever developed a rash. People who are sensitive to urushi can protect themselves by wearing latex, nitrile, or rubber gloves that are easily obtained. Therefore, we should be able to use urushi casually. We have already developed a new method for DIY to add a pattern to an urushi-coated surface by controlling the UV light direction [7].

Conclusion We proposed an urushi circuit that uses a traditional craft material for human-computer interfaces (HCIs). To achieve our goal, we proposed a method for fabricating an urushi circuit by UV laser, and confirmed the feasibility of our method. We also fabricated prototype output and input circuits, and verified that these worked. As future work, we will improve our method to fabricate more precise circuits. We will also develop an urushi-based interface system that includes all parts (e.g., a microcomputer, analog circuit, input and output parts, etc.) of a HCI.

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Yuki HASHIMOTO He is currently an Assistant Professor of the Faculty of Engineering, Information and Systems, University of Tsukuba. He received the Ph.D. Eng. from The University of Electro Communications, Tokyo, Japan, in 2010. His research interests span the field of interactive technology, virtual reality, haptic interface and tele-existence.